By studying a group of patients examined during the last nine years at the Dermatology Clinic of the State University of Rome, it has been possible to verify a statistically significant decrease in the percentage of patients reactive to patch tests of aniline, paraphenylenediamine (PPDA), and procaine hydrochloride, during the last three-year period, 1962 to 1965, with respect to the previous three-year periods, 1956 to 1959 and 1959 to 1962.
Cobalt sensitivity showed a marked increase during the period 1959 to 1962 followed by a return to baseline levels.
Substantial variations in sensitivity to nickel and, probably, also potassium bichromate were not demonstrable over a similar time period.
SCARPA C, FERREA E. Group Variation in Reactivity to Common Contact Allergens. Arch Dermatol. 1966;94(5):589–591. doi:10.1001/archderm.1966.01600290063010
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